Group Members: Kareem Hussein Tatiana Kresefsky Sita Keita Joan Lee Lab 2 pH/ Buffer Assignment Alternative pH data Graph Buffer Action A buffer is defined as a solution that resists changes in pH when small amounts of acid or base are added. A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, The pH of cells and tissues in animals and plants is tightly regulated. Large changes in pH are extremely detrimental to an animal. In particular the pH of the blood must be kept within very narrow bounds. There are several buffer systems for blood pH alone, bicarbonate, phosphate and protein based buffers. A buffer is made by mixing a weak acid with its salt so that this solution can act as an acid (give up H3O+) and act as a base (accept H3O+). The more concentrated the buffer solution, the greater its buffer capacity. ... If the buffer capacity is 10 times larger, then the buffer solution can absorb 10 times more strong acid or base before undergoing a significant change in pH. The buffer range is the pH range where a buffer effectively neutralizes added acids and bases, while maintaining a relatively constant pH. The buffer capacity is optimal when the ratio is 1:1; that is, when pH = pKa. For the combined solutions line, indicate those buffering range and optimal capacity. This may be done using the computer or by hand or using the already drawn graph. Your objective is to test a prediction (if/then question) that supports a hypothesis. Your conclusion is based on the above data generated in lab. Use numbers to describe what you see and whether what you see supports your conclusions. Questions 1. Explain the range of pH over which it buffers and why it buffers over this range. The range of pH is unique to every buffer and its own unique feedback system. With an effective buffer, a constant pH is maintained even with the addition of acid or base. It buffers over this range because this is where it is able to effectively maintain a constant pH through the neutralization of any addition of acids or bases. An example of the importance of pH range is the pH buffer system for blood, which through bicarbonate, phosphate, and other important players, the blood can maintain a pH in the range of 7.35 and 7.45. It buffers over this range because an extremely high pH can lead to alkalosis, while a low blood pH can lead to acidosis. It works over this range because the buffer is made through the mixing of a weak acid with its salt, allowing the solution to either act as a base by accepting hydronium or giving hydronium up in an attempt to lower pH. 2. Explain what the buffering capacity of a solution means? The buffering capacity of a solution is the amount of strong acid or strong base that can be added without changing the pH by more than 1 pH unit. It measures how efficient a buffer solution is to pH changes. It depends on the amount of weak acid and its conjugate base in a buffer solution. 3. If a solution has no buffering capacity, explain why it does not. If the log of the conjugate base divided by the acid is greater than 1, this would signify that there is no buffer. This would happen if the value of the base was more than 10 times greater than that of the acid. This could also happen if the acid is more than 10 times greater than the base. The conjugate acid/ base in those scenarios wouldn’t be strong enough to create an effective buffer. 4. How can a chemical buffer both acid and base? Buffer is a solution that contains weak acid and its conjugate base, or weak base with its conjugate acid. Buffers neutralize any added acid or base to moderate pHby making them a weaker acid or base. For example, when a strong acid is added to a buffer system, the hydrogen ions will be consumed by the conjugate form of the added strong acid. The added acid will be weaker and the pH of the solution will not change significantly. 5. What is the Equivalence point? The equivalence point is where the amount of titrant added is enough to completely neutralize a solution during titration. For the write-up, the major emphasis is on a quantitative discussion of results. 6. What does graph tell you about the ability of a chemical to act in terms of capacity and range as a buffer? You have a mathematical description of this in the Henderson Hasselbalch equation. A solution has a capacity to act as a buffer within the +/- 1 pH range of the solution. If the solution is too acidic, the buffer won’t be able to maintain equilibrium and the pH will drop. If the solution is too basic, the buffer won’t be able to maintain the equilibrium and the pH will rise. This can be seen in the gray line on the graph. The pH tapers out around -6 until approximately +7. Outside of that range, too much acid/base has been added to the buffer and it exceeds capacity. This is when you see a significant change in the pH. pH= pKa + log (Conjugate base/ Acid)
